Margarines have gained wide consumer acceptance as a substitute for butter. Consumers frequently prefer margarine over butter because margarine is usually less expensive than butter and generally has a lower proportion of saturated fats than butter. However, in spite of a vast amount of research in developing butter flavorings for margarines, consumers generally prefer the taste of butter to the taste of margarines previously available. Even premium grades of margarine have been described as "chemical" or "synthetic" in flavor. Indeed, recently blends of margarine and butter have been introduced commercially in order to provide a product which has at least some of the advantages of margarine but which has a more satisfactory butter taste.
One of the many components of natural butter flavor is the compound diacetyl, which is a ketone having a characteristic "buttery" aroma. It has been known that diacetyl in dairy products is generally produced by the fermentation of milk citrates by bacteria of the Leuconostoc species and the Streptococcus diacetilactis strain. M. Y. Pack et al. J. Dairy Science, vol. 51, pp. 339-344 (1967). It has been observed that fortifying milk with additional citrate can enhance the production of diacetyl by certain dairy cultures growing in the milk. E. B. Collins, J. Dairy Science, vol. 55, pp. 1022-1028. The addition of citric acid to a culture of Leuconostoc cremoris growing in a medium of skim milk fortified with yeast extract gave rise to the production of diacetyl and a related compound, acetoin, whereas no diacetyl or acetoin was produced by the culture when no citric acid was added. T. M. Cogan, J. Dairy Res., vol. 42, pp. 139-146(1975).
Cultured dairy products such as cottage cheese are often produced using "starter cultures" of microorganisms. The microorganism which is to convert milk or a milk derivative into the desired cultured dairy product is first grown in a suitable medium to form a starter culture. When the population of the microorganism in the starter culture is sufficiently high, the starter culture is added to the milk or milk derivative. Liquid cheddar-cheese whey combined with certain inorganic phosphates and other compounds has been used as a medium for starter cultures. N. Ausavanodom et al., J. Diary Science, vol. 60, p. 1245-1251 (1977).
Certain types of starter cultures can be distilled to produce a starter-culture distillate which is used as a flavor additive in margarine and other foods. Pack et al. supra, page 344. However, as noted above, the flavors of even premium grades of margarine heretofore available leave much room for improvement.